Welcome to the Goldfarb Lab Homepage
In the Department of Pathology at the University of Virginia
We are located on the third floor of the MR5 building in the Department of Pathology at the University of Virginia. Our interest is in the molecular mechanisms underlying human blood cell development in the bone marrow. We have focused on trying to understand the earliest stages involved in the generation of megakaryocytes, the large cells with multilobulated nuclei responsible for platelet production.
Understanding how megakaryocyte developement is programmed has major clinical importance. Cancer patients treated with high-dosage chemotherapy often have poor megakaryocyte regeneration in the bone marrow, leading to a dependency on large numbers of platelet transfusions. Growth factor treatments are available to enhance red cell and white cell regeneration, but no agents exist that enhance megakaryocyte/platelet regeneration.
Our lab has recently discovered that megakaryocyte development actually represents an offshoot of red cell (erythroid) development. In particular, we have found that human marrow cells developing along the red cell pathway can be re-programmed to enter the megakaryocytic developmental pathway (see below). As a means to harness this plasticity for clinical use, we have begun to unravel the signaling pathways that prompt megakaryocyte divergence away from the erythroid lineage:
Evidence of erythroid potential for megakaryocytic transdifferentiation. Primary human erythroid progenitors were purified by flow sorting for glycophorin A positive cells; the starting population was almost 100% positive for hemoglobin expresssion (green fluorescence). Incubation of these cells in conditioned medium from leukemic cells undergoing megakaryocytic differentiation (cond. medium) induced the rapid up-regulation of the megakaryocytic glycoprotein IIb(gpIIb). Frequent cells showed hybrid phenotypes with coexpression of hemoglob in and gpIIb (arrows). By contrast, growth of the starting population in standard megakaryocytic medium with thrombopoietin (TPO) did not lead to megakaryocytic outgrowth.
Critical nodes in the regulator circuitry include the Rap1 small GTPase and the ERK/MAPK signaling pathway, transcription factors of the GATA family, transcription factors of the RUNX family, and the bone marrow stromal microenvironment. Each of these components is a subject of investigation in the laboratory. Experimental approaches apply current techniques in molecular biology, cell biology, protein chemistry, and pharmacology.
Critical determinants of erythroid-megakaryocytic lineage divergence. Both lineages arise from a common progenitor cell, the BFU-E/Mk, also known as the MEP (megakaryocytic-erythroid progenitor). Transcription factors of the GATA, FOG, SCL/tal, and NF-E2 families are critical for differentiation of both lineages. The RUNX1 transcription factor and the Rap1 signaling molecule appear to promote megakaryocytic lineage separation. The leukemic onco-protein RUNX1-ETO blocks both erythroid and megakaryocytic differentiation.
